A new unicuspid-toothed species of Hypostomus Lacépède , 1803 ( Siluriformes : Loricariidae ) from the rio Paraguai basin

A new unicuspid-toothed armored catfish species of Hypostomus is described from the Bodoquena Plateau, rio Paraguai basin, Mato Grosso do Sul State, Brazil. The new species is distinguished from its congeners, with exception of H. fonchii, by having unicuspid teeth (vs. bicuspid teeth); from H. fonchii it is distinguished by having median series of lateral plates with 26-27 (vs. 28); by lower number of premaxillary and dentary teeth (7-10 vs. 18-21; 8-13 vs. 18-25, respectively); for possessing more depressed head (head depth 15.8-18.1% SL vs. 19.1-22.0% SL); and by the presence of median buccal papilla (vs. absence).

The Bodoquena region is drained by the Apa, Formoso, Formosinho, Perdido, Miranda, rio do Peixe, Salobra, and Sucuri rivers, all part of the rio Paraguai basin (Boggiani, 1999;Salles et al., 2006).According to Boggiani (1999) some of those rivers flow through calcareous terrain resulting in a low turbidity and very clear waters.The region is known for its large aquatic biodiversity and endemism (Scremin-Dias et al., 1999).Sabino & Trajano (1997) described Ancistrus formoso, an albino cave dwelling armored catfish and, then, ten years later Ribeiro et al. (2007) published the discovery of a new characin Oligosarcus perdido from that region.
Examination of specimens of the genus Hypostomus from the rio Perdido, a tributary to rio Apa of the rio Paraguai basin, revealed a population with an unusual pattern of unicuspid teeth.The aim of this paper is to establish it as a new species of Hypostomus from the Bodoquena Plateau.

Material and Methods
Measurements were made with digital calipers to the nearest 0.1 mm.Methodology and terminology for measurements DOI: 10.1590/S1679-62252014000100010 follow Boeseman (1968) with modifications by Weber (1985) and Zawadzki et al. (2008).Plate counts and nomenclature follow Schaefer (1997), with the modifications of Oyakawa et al. (2005).Vertebral counts were taken on cleared-andstained (c&s) specimens, according to Taylor & Van Dyke (1985) procedures.The vertebral complex of the Weberian apparatus and the compound caudal centrum were counted as a single element (Lundberg & Baskin, 1969).Osteological nomenclature follows Schaefer (1987).Standard length (SL) is expressed in millimeters; some measures are expressed as percents of SL; some as percents of head length (HL) and additionally, some other percents are according to Zawadzki et al. (2010).Meristic and morphometric ranges of the type series of Hypostomus fonchii Weber & Montoya-Burgos cited in the diagnosis section of the present work are from Weber & Montoya-Burgos (2002) Dorsal fin II,7; distal margin slightly convex to straight; origin at vertical two plates before pelvic-fin insertion; adpressed rays not reaching adipose-fin spine.Pectoral fin I,6; distal margin straight and almost reaching from one-third to half pelvic-fin length, odontodes more developed on distal dorsal region.Pelvic fin I,5; distal margin straight to slightly convex; distal portion of unbranched pelvic-fin ray reaching or slightly surpassing anal-fin insertion when adpressed to body.Anal fin I,5; distal border rounded.Caudal fin I,14,I, posterior margin truncate to slight emarginated; lower lobe slightly longer than upper lobe.Vertebrae 27; ribs 9, first rib relatively larger than others.
Dorsal and lateral surface of head and body covered with dermal plates, except snout tip and area surrounding dorsal-fin base.Plates on lateral margin of head, from snout tip to pterotic-supracleithrum small and irregular.Five lateral series of plates on trunk.Dorsal, mid-dorsal, median, midventral and ventral series without keels.Lateral line complete on median lateral series.Mid-ventral series moderately bent on anterior portion.Ventral region of body with small platelets bearing odontodes, except area beneath lower lip, insertion of pectoral and pelvic fins, and anterior region of grayish brown.Trunk and fins densely covered by faint darker spots; spots smaller on head and larger on fins and posterior portions of body.All spines and unbranched-fin rays with spots.Dorsal, pectoral, and pelvic fins with one series of spots on each interradial membrane.Dorsal-fin spots usually larger than spots in remaining fins and usually aligned to form five to seven horizontal bands; spots mottled in some specimens.Anal-fin spots more faded than remaining fin spots.Abdominal region pale yellowish.Ventral surface of body and paired fins spotless.
Distribution.The new species is known from its type locality, the rio Perdido, tributary to the rio Apa, rio Paraguai basin, Mato Grosso do Sul State, Brazil (Fig. 3).
anus.Naked areas reduced on larger specimens.Lips round; covered with dense papillae, which decrease in size to distal border.Median buccal papilla sensu Armbruster (2003, fig. 3) present.Buccal skin internally bordering premaxilla and dentary with unorganized series of flat enlarged papillae (Fig. 2a,c).Maxillary barbel elongate and proximately joined to labial border by membrane; distal tip free.Premaxilla with 7 to 10 teeth, dentary 8 to 13 teeth; teeth robust, moderate in length, unicuspid, crown short and continuous to stalk (without notch between stalk and crown).Dentary rami straight and angled 82 to 94° from each other (n = 20 specimens; mean = 85.8°).mainly due to suspended clay.Specimens of Hypostomus perdido were collected in stretches of sluggish to still waters.
Etymology.The specific name perdido alludes to the type locality rio Perdido.From the Portuguese "perdido", which means lost.An adjective nominative, masculine, and singular.

Discussion
The unusual teeth morphology of Hypostomus perdido distinguishes the new species not only from its congeners from the rio Paraguai basin, but from nearly all species of the genus.The only exception is H. fonchii, described from the west tributaries to the middle río Ucayali in Peru, which also has unicuspid teeth (Fig. 2b and 2d).Hypostomus fonchii (Fig. 4) also inhabits Bolivian streams flowing to the rio Mamoré.Despite the tooth similarity, H. perdido is more depressed than In the plateau, the river is 10 to 12 m wide and is dammed by several calcareous tufa deposits, some of them forming waterfalls from one to five meters high.The dammed sections can be as deep as 12 m, with vertical rock banks and very slow flow; the substrate is a whitish calcareous clay on which lay many submerged logs, branches and even whole trees.The water is very clear throughout the dry season.However, transparency is significantly reduced in the rainy season, rounded snout (vs.triangular).In addition, the new species presents dentary rami angled to each other from 82 to 94° versus less than 80° in the species of the H. cochliodon group.To elucidate the phylogenetic relationships of the new species a cladistic analysis based on morphological and/or molecular data would be necessary.However, considering the aforementioned differences, it would be plausible that unicuspid teeth character had arisen independently.Cytogenetic data are already available to Hypostomus perdido.The species was named as "Hypostomus sp 2-Rio Perdido NUP 4249" by Cereali et al. (2008).Except H. perdido, the diploid number in Hypostomus ranges from 54 to 82 (Bueno et al., 2012).Cereali et al. (2008) found H. perdido with 84 chromosomes (2n = 84), as the greatest diploid number known in Hypostomus (Martinez et al., 2011;Rubert et al., 2011;Endo et al., 2012;Bueno et al., 2013).H. fonchii, has less dermal plates on the median series and less teeth on premaxilla and on dentary.Weber & Montoya-Burgos (2002) addressed H. fonchii to the H. cochliodon group due to its unicuspid tooth pattern.Armbruster (2003) noted that the species of H. cochliodon group did not possess unicuspid teeth but bicuspid teeth with lateral cusp usually fused to mesial cusp and rejected a close relationship with H. fonchii because the body morphology did not agree with the typical body shape of the members of the H. cochliodon group.Armbruster (2003) also commented that specimens of H. fonchii were not examined by him, in that work.Herein, we verified the tooth morphology of H. fonchii finding clearly unicuspid teeth, but it is anyway much slender than the teeth of H. perdido.Montoya-Burgos et al. (2002) performed a phylogenetic analysis based on mitochondrial D-loop sequences data and recovered Hypostomus fonchii within the H. cochliodon group of species, corroborating the initial proposition of Weber & Montoya-Burgos (2002).The position of H. fonchii within the H. cochliodon group of species was also maintained in Montoya-Burgos (2003).Therefore, we consider H. fonchii somewhat morphologically compatible with the H. cochliodon group species.Contrary to H. fonchii, H. perdido indeed does not resemble representatives of the H. cochliodon group of species, since it possesses slender body (vs.robust) and
Ecological notes.The upper 50 km of the rio Perdido flows from elevations of 550 m to 350 m through the calcareous Bodoquena Plateau.It initially flows to the southeast, passes about 2 to 3 km as subterranean portion, then turns roughly southwards and bisects the Parque Nacional da Serra da Bodoquena, where the river flows confined in open folds of the Paraguai Fold Belt.Then the river turns to the southwest, descends the plateau escarpments and flows 250 km further before discharging in the rio Apa, at roughly 100 m altitude.

Fig. 3 .
Fig. 3. Distribution of Hypostomus perdido.Red star symbol represents its type locality, the rio Perdido, rio Paraguai basin, Mato Grosso do Sul State, Brazil.Inset in the right upper corner highlights the area into a South American perspective.
rio Paraguai basin, rio Perdido, 21°17'09"S 56°41'47"W, 8 Sep 2005, O. Froehlich.Paratypes.All collected with the holotype (61 specimens).ANSP 193370, 2, 163.6-171.3mmSL.CPUFMT 1500, 2, 152.5-170.3mmSL.INPA 37689, 1, 144.4 mm SL.MCP 47141, 2, 133.9-147.9mmSL.Diagnosis.Description.Measurements and counts in Table1.Dorsal profile of head convex from tip of snout to supraoccipital posterior end; straight from that point to dorsal-fin origin.Head elevated and compressed.Snout narrow and compressed, covered by irregular series of several small plates.Mesethmoid forming conspicuous bulge from snout tip to nares.Upper orbital margin not elevated.Eye laterodorsally positioned.Interorbital region wide and flat in frontal view.Very slender keel on upper portion of pteroticsupracleithrum just posterior to orbit.Opercle considerably large and somewhat ellipsoidal; its horizontal length similar to orbital diameter; odontodes slightly larger on posterior margin.Predorsal region almost flat; usually with one single larger plate surrounding supraoccipital followed by two narrow plates in front of dorsal-fin spinelet.Dorsal profile of trunk tapering straight from dorsal-fin insertion to caudal peduncle posterior portion; ascending to caudal fin.Adipose fin long, almost same length of minimum caudal peduncle depth.Maximum body width at region of dorsal-fin origin; profile gradually tapering from this point to caudal fin.Caudal peduncle somewhat ellipsoid in cross-section; dorsal and ventral caudal peduncle region slightly flattened.